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Chapter 5

PSY210 textbook notes chapter 5

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Elizabeth Johnson

[LECTURE 4] CHAPTER 5: THE  CHILD’S GROWTH BRAIN ,BODY ,MOTOR  SKILLS AND  SEXUAL MATURATION BRAIN DEVELOPMENT IN INFANCY I. The prenatal period a. Brain grows rapidly b. Infant’s brain weighs ¼ as much as a mature brain, a 6 month old’s weighs ½, and a 2 year old’s weighs ¾ II. Largest portion of the brain consists of two connected hemispheres that make up the cerebrum (the two connected hemispheres of the brain) a. The covering layer of the human cerebrum (the cerebral cortex) i. Highly convoluted and contains about 90% of the brain cell’s bodies ii. Contains the cells that control specific functions like seeing, hearing, moving, and thinking NEURONS AND SYNAPSES I. Baby’s brain has most of its neurons at birth II. During the embryonic period, neurons multiply at a rapid pace in a process called neuron proliferation a. Neurons: a cell in the body’s nervous system consisting of a cell body, a long projection called an axon, and several shorter projections called dendrites; neurons send and receive neural impulses, or messages, throughout the brain and nervous system b. Neuron proliferation: the rapid proliferation (multiplication) of neurons in the developing organism’s brain III. Brain gets bigger b/c existing neurons grow and the connections between them proliferate IV. Glial cells a. Surround and protect neurons b. Also grow c. Provide neurons with structural support, regulate their nutrients, and repair neural tissue d. Some are responsible for myelination i. Parts of neurons are covered with layers of a fatty, membraneous wrapping called myelin ii. Makes the neuron more efficient in transmitting information iii. Most myelination occurs during the first two years of life but continues into adulthood V. Neurons are constantly moving VI. Neural migration is guided by neurochemical processes a. Ensures that all parts of the brain are served by a sufficient number of neurons b. Absence of sufficient neurons in their proper locations is associated w/ various forms of mental disability and disorders like dyslexia and schizophrenia VII. Synapses: connections b/w neurons a. the extended axon of one neuron transmits a message to the projected dendrites of another neuron, usually by means of chemicals that cross the small space b/w neurons b. crucial to surviving and learning i. as the brain’s neurons receive input from envt they create new synapses, allowing for complex communications VIII. Synaptogenesis: forming of synapses a. beings early in prenatal life (as soon as neurons begin to evolve) b. brain forms more synapses than neurons IX. 2 processes reduce the number of neurons and connecting fibres i. Neuronal death: death of some neurons that surround newly formed synaptic connections among neurons to make space for the new information ii. Synaptic pruning: the brain’s disposal of the axon and dendrites of a neuron that is not often stimulated; frees up space for new synaptic connections b. Increases speed, efficiency, and complexity of transmissions b/w neurons and allows room for new connections that develop as the child encounters new experiences SEQUENTIAL DEVELOPMENT OF THE BRAIN I. There is an orderly sequence to brain development during infancy a. Early months of life: move from mostly reflexive behaviour to voluntary control of movements i. Motor area of brain develops most rapidly b. 2 months old: motor reflexes (rooting, startle response) drop out and motor cortex begins to oversee voluntary movement (reaching, crawling, walking) i. In the visual cortex, the number of synapses per neuron is multiplied some six times within the first two years of life ii. Infants’ visual capacities are greatly enhanced (ex. become more skilled at focusing on objects at different distances) HEMISPHERIC SPECIALIZATION I. Hemispheres: the two, left and right, halves of the brain’s cerebrum a. Anatomically different b. Control different functions II. Corpus callosum: the band of nerve fibres that connects the two hemispheres L EFT AND  R IGHT  B RAIN  FUNCTIONS I. Hemispheric specialization: differential functioning of the two cerebral hemispheres II. Left hemisphere of motor cortex controls simple movement in the right side o the body III. Right hemisphere controls the body’s left side IV. Lateralization: the process by which each half of the brain becomes specialized for the performance of certain functions a. Right hemisphere i. processes visual-spatial information, non-speech sounds (music), perception of faces 1. If damaged, drawing skills may deteriorate, trouble following maps or recognizing friends, spatial disorientation ii. Processing emotional information 1. If damaged, can have difficulty interpreting facial expressions 2. Left hemisphere is activated in the expression of emotions associated with approach to the external environment (joy, interest, anger) 3. Right hemisphere is activated in emotional expressions that cause the person to turn away or withdraw from that environment (distress, disgust, fear) b. Left hemisphere i. Associated w/ language processing 1. People w/ damage may have trouble understanding what is said to them or speaking clearly 2. In deaf persons who use sign language (motor movements of hands) – right side of brain takes over language functions 3. Possible better processing of auditory and musical pitches C ONSEQUENCES  OF  BRAIN  LATERALIZATION I. Dyslexia: a term for difficulties experienced by some people in reading or learning to read a. Difficulty integrating visual and auditory information (ex. matching written letters or words to their sounds) b. Suggested that children w/ dyslexia don’t show normal lateralization pattern i. Process spatial information on both sides of the brain rather than primarily on the right, and thus their left hemispheres may become overloaded ii. Leads to deficits in language skills II. Handedness – another lateralized function a. 90% of adults are right handed and a majority of infants show right hand dominance b. Gene for handedness identified c. Many left handed people are ambidextrous – suggests brains may be less clearly lateralized than brains of right handed people THE BRAIN'S PLASTICITY: EXPERIENCE AND BRAIN DEVELOPMENT I. Plasticity: capacity of the brain, particularly in its developmental stages, to respond and adapt to input from the external environment II. 2 types of experience influence brain development a. Experiences like touch, patterned visual input, sounds of language, affectionate expressions from caregivers, nutrition i. All expected in normal environment ii. Trigger synaptic development and pruning iii. Critical for normal brain development iv. When there’s an interference, basic abilities are impaired 1. Ex. when children have congenital cataracts, their visual system is deprived of stimulation and fails to develop properly 2. When cataracts are removed, the adult is blind b. Experiences that are unique to individuals i. Encountered in particular families, communities and cultures ii. Brains respond to different environments by developing synaptic connections that encode specific and unique experiences 1. Ex. children in Mozambique develop aspects of the motor cortex that correspond to the skills associated w/ hunting and fishing 2. North American children develop parts of the brain that reflect the fine motor and eye hand coordination needed for success at video games III. Animal research shows that the size, structure, and biochemistry of the brain can be modified by experience a. Rosenzweig study i. Placed rats in 2 dif environments ii. ‘enriched’ envt w/ large, brightly lit communal cages with wheels and toys iii. ‘impoverished’ environment where each rat was alone in a bare cage in a dim room iv. Discovered that after 3 months, the weight of the cerebral cortex (controls higher-order processes) was 4% heavier for rats in enriched environment, and the weight of the occipital region (controls vision) was 6% heavier v. Enriched envt tends to increase the complexity of neurons as measured by the number of dendrites they develop 1. More dendrites = more synapses with other neurons 2. More information can be sent via these synaptic connections 3. Activity of key chemicals in the brain (esp in cerebral cortex) increases as a result of an enriched environment b. Adult rats exposed to impoverished or enriched envts after being reared in regular lab conditions show changes similar to those of young rats IV. Research on human infants also demonstrates the brain’s plasticity a. Infants respond to the sounds of all languages b. Become more selective over first year of life, responding increasingly to sound of own language c. Dif sets of neuronal connections become programmed to respond to particular aspects of speech, so infants’ brains develop ‘auditory maps’ or templates to respond to certain auditory features and not others V. Exposure to music can enrich brain development a. Natural harmonics of music may help brain develop a wiring diagram that promotes spatial- temporal reasoning b. Piano study i. After 6 months of weekly piano lessons, 3 and 4 year olds improved in this kind of reasoning as demonstrated by their ability to look at disassembled picture of an elephant and to know how to put it together ii. Children who received computer training or no stimulation showed little improvement VI. Some research demonstrates that the brain can undergo structural change based on unique experiences even in adulthood a. Looked at structure of brains of humans w/ extensive navigational experience (London taxi drivers) and compared w/ control subjects who did not drive taxis b. Found that the posterior hippocampi (associated w/ spatial representations of the envt) was larger in taxi drivers c. Suggests a remarkable degree of plasticity in the brain structure in response to envt demands VII. Lack of stimulation and exposure to traumatic events can damage the brain and cause it to malfunction a. In abused children the cortex and the limbic system (involved in emotion and infant parent attachment) are 20-30% smaller and have fewer synapses than non abused children b. Techniques such as PET scans (positron-emission tomography) also show the effects of early deprivation on the developing brain i. Under unstimulating and unresponsive envts, there is a reduced connectivity or communication between regions of the brain ii. Reduced cortical activity involving neurons acting together to solve a cognitive task such as memory or face processing MOTOR DEVELOPMENT HAND SKILLS I. Newborns display a grasping reflex and rudimentary form of reaching - ‘prereaching’ a. Involves uncoordinated swipes at objects they notice II. At 3 months, infants initiate a more complex and efficient pattern – ‘directed reaching’ III. By 5 months, generally succeed in reaching in for an object and successfully grasping it a. Involves muscle growth, postural control, control of movement of arms and hands IV. How reaching develops is consistent with the dynamic systems view of development (from chapter 1) a. One component of the dynamic system is visual perception i. If infant has nothing to look at, there’s no incentive to reach out b. Another component involves the motor ability to grip an object i. 4 month olds use touch to determine their grip while 8 month olds use vision (can preshape hand as they reach for an object) V. Over the first year of life, infants’ progress in controlling their hands is remarkable (become highly skilled reachers) a. Begin to use objects as tools b. Learn the use of gestures in social communication c. By age 2, use hands in play (ex. building a tower) d. By age 3, use hands to scribble with crayons LOCOMOTION I. Development of locomotion involves 3 phases a. 1 : when you hold a baby upright and let his feet touch a flat surface, tilting his body from side to side, the baby responds by reflexively moving his feet in a rhythmic stepping motion i. Reflex disappears by 2 months old nd b. 2 : during the second half of baby’s first year; reappearance of stepping movements rd c. 3 : about 1 year; infants begin to walk without support II. Theories of how walking develops a. Maturational theorists i. Depends on development of the motor cortex b. Cognitive theorists i. response to cognitive plans or representations that are the consequence of watching other people walk c. Thelen’s dynamic systems theory i. Walking skills are determined by the interplay of a variety of factors (Ex. emotional, postural) ii. Newborn stepping response disappears for 10 months before true walking emerges b/c of anatomical factors 1. Baby’s size and weight become too much of a load on emerging motor system rd III. Running well established by the 3 year IV. Hopping emerges b/w 2 and 3 years V. These skills depend on improvements in balance and coordination and the opportunity for practice HOW LOCOMOTION MAY AFFECT OTHER ASPECTS OF DEVELOPMENT I. Increased independence as result of ability to walk a. Can explore envt more fully and initiate more contact w/ other people b. Leads to increased parent-child interaction – babies can move from place to place and make a mess/get into a dangerous situation II. ‘perception-action coupling’ approach a. Motor/action systems are functionally interrelated to sensory or perceptual systems such that changes in one aspect influence the development of the other aspect b. Locomotion can change the way babies understand their perceptual world i. Ex. beginning of crawling = fear of heights, spatial abilities c. Locomotion possibly helps infants deal better w/ changes in spatial orientation i. Study where crawling babies were better at precrawling babies at finding a hidden toy that was moved III. ‘moving room’ experiments a. Room in which walls and ceilings can be moved back and forth while the floor stays immobile b. 3-6 year olds will only sway back and forth to visual movement c. Self produced locomotion is critical for infants’ use of visual information in such situations i. Crawling infants but not precrawling ones used moving room input to control their balance THE ROLE OF EXPERIENCE AND CULTURE I. Cross cultural studies a. When parents give babies special physical attention (massage, exercise) infants achieve motor milestones somewhat earlier i. Zambia – mothers carry new babies in sling on backs; when sitting, leave infants sitting alone, where they can practice the development of motor skills ii. Jamaica – mothers massage infants, stretch arms and legs, let practice stepping; children also are motorically advanced iii. Zinacantecos of Mexico – infants tightly swaddled for first 3 months, have less advanced motor skills iv. Chinese families – babies put on pillows, crawling restricted; some infants fail to develop adequate strength in muscle groups critical for crawling; crawling is delayed II. Geographic region where children are reared may influence motor development a. Infants born in summer months or fall months acquired motor skills later than winter-spring infants b. Summer/fall infants would begin developing motor skills in winter time when there are shorter days, cold temperatures and restrictive clothing (more difficult to move) PHYSICAL GROWTH I. Study of physical growth is guided by 2 classic principles a. Growth characterized by cephalocaudal development i. Growth occurs from the head downward ii. Brain and neck develop earlier than legs and trunk b. Growth follows a proximal-distal pattern i. Centre outward ii. Internal organs develop earlier than arms and hands II. Height and weight a. 2 principal measures of overall growth b. Babies grow faster in first half of life than ever again c. Nearly double their weight in first three months and triple it by end of first year d. Top heavy light bulb shaped bodies become cylindrical e. Centre of mass moves from sternum to below the belly button f. Growth is epi
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